1. Field
Exemplary embodiments of the present invention relate to a semiconductor design technology, and more particularly, to a duty cycle correction circuit and an image sensing device including the duty cycle correction circuit.
2. Description of the Related Art
Semiconductor devices use clocks to perform operations at specific times. For example, a semiconductor device may perform an operation based on one or both of the rising and falling edges of a clock.
Efforts to correct clock duty cycles have been made to improve operation margin and high-speed operation. The duty cycle of the clock is the ratio of the logic low level duration to the logic high level duration. It is important to precisely control the duty cycle of the clock to be 50:50 so that valid window regions of signals and data are secured. Clock duty cycle is an important factor in determining the performance of the semiconductor device.
Accordingly, semiconductor devices include a duty cycle correction circuit for correcting clock duty cycles. For example, a duty cycle correction circuit may correct the duty cycle of a clock outputted from a delay locked loop (DLL) a phase locked loop (PLL), a rising voltage controlled oscillator (VCO) and so on included in the semiconductor device at a ratio of 50 to 50. The corrected clock having a duty cycle of 50:50 becomes the basis for stable circuit operations.
However, duty cycle correction circuits generally require a large amount of circuit area, have complicated structures, and have high current consumption.
A semiconductor device may also include an image sensing device, and the image sensing device may include a duty cycle correction circuit for using a double data rate (DDR) scheme. For example the image sending device may perform a counting operation based on the DDR scheme using a clock for converting a pixel signal outputted from a pixel into a digital signal. In order to properly perform the counting operation based on the DDR scheme, it is important to use a clock having a duty cycle of 50 to 50.
An image sensing device captures images using the photosensitive properties of semiconductors. Image sensing devices may be classified into charge coupled device (CCD) image sensors and complementary metal oxide semiconductor (CMOS) image sensors. CMOS image sensors have come into widespread use. This is because CMOS image sensors allow analog circuits and digital control circuits to be directly implemented on a single integrated circuit (IC).